Myosins are molecular motors that, upon interaction with actin filaments, utilize energy from ATP hydrolysis to generate mechanical force.
Phylogenetic analysis of the myosin motor domains identified 11 distinct classes, 7 of which are expressed in vertebrates.
These 7 vertebrate myosin classes include conventional myosin (myosin II) and 6 less well characterized unconventional myosin classes, myosins I, V (MIM.160777), VI (MIM.600970), VII (MIM.276903), IX, and X (MIM.601481).
Each myosin has a conserved N-terminal motor domain (25 to 40% identical at the amino acid level) that contains both ATP-binding and actin-binding sequences.
Following the motor domain is a light-chain-binding 'neck' region containing 1-6 copies of a repeat element, the IQ motif, that serves as a binding site for calmodulin (MIM.114180) or other members of the EF-hand superfamily of calcium-binding proteins.
At the C terminus, each myosin class has a distinct tail domain that serves in dimerization, membrane binding, protein binding, and/or enzymatic activities and targets each myosin to its particular subcellular location.
Structure
In vertebrate striated muscle, myosin is composed of 2 heavy chains of about 200,000 daltons each (myosin heavy chains - MYHs) and 4 light chains of about 20,000 daltons each (mysoin light chains - MYLs).
Phylogenetic analysis of the myosin heavy chains motor domains identified 11 distinct classes, 7 of which are expressed in vertebrates. These 7 vertebrate myosin heavy chains classes include conventional myosin (myosin II) and 6 less well characterized unconventional myosin classes, myosins I, V, VI, VII, IX, and X.
Members
myosin-I | MYO1A | MYO1B | MYO1C | MYO1D | MYO1E | MYO1F |
myosin-II | MYO2 | |||||
myosin-III | MYO3 | |||||
myosin-IV | MYO4 | |||||
myosin-V | MYO5A | MYO5B | ||||
myosin-VI | MYO6 | |||||
myosin-VII | MYO7A | MYO7B | ||||
myosin-VIII | MYO8 | |||||
myosin-IX | MYO9A | MYO9B |
Structure
Each myosin has a conserved N-terminal motor domain (25 to 40% identical at the amino acid level) that contains both ATP-binding and actin-binding sequences.
Following the motor domain is a light-chain-binding 'neck' region containing 1-6 copies of a repeat element, the IQ motif, that serves as a binding site for calmodulin or other members of the EF-hand superfamily of calcium-binding proteins. At the C terminus, each myosin class has a distinct tail domain that serves in dimerization, membrane binding, protein binding, and/or enzymatic activities and targets each myosin to its particular subcellular location.
MYO1A | autosomal dominant nonsyndromic deafness | |
MYO5A | Griscelli disease | |
MYO6 | recessive deafness DFNB37 | |
MYO7A | Usher syndrome type I | MIM.276903 |
MYO9B | celiac disease susceptibility | MIM.609753 |
References
Matsumura F. Regulation of myosin II during cytokinesis in higher eukaryotes. Trends Cell Biol. 2005 May 31; PMID: #15935670#
Karcher RL, Deacon SW, Gelfand VI. Motor-cargo interactions : the key to transport specificity. Trends Cell Biol. 2002 Jan ;12(1):21-7. PMID : #11854006#
Rodriguez OC, Cheney RE. A new direction for myosin. Trends Cell Biol. 2000 Aug;10(8):307-11. PMID: #10884682#
Mermall V, et al: Unconventional myosins in cell movement, membrane traffic and signal transduction. Science 279:527, 1998.